Phase 1-3 of the builder subsystem on the Mac mini:
- Express + SQLite + sessions scaffolding, LAN-only service on port 3090
- App Store Connect JWT client (ES256 signing, devices/profiles/bundleIds)
- Device management UI with Apple-side registration
- Fastlane sigh wrapper with profile cache + auto-install to ~/Library/
- launchd plist + deploy script for Mac mini supervision
